Quantum dot sheet of fibrous-web structure, manufacturing method thereof, and backlight unit

ABSTRACT

A quantum dot sheet having a fibrous-web structure, including a quantum dot layer having a three-dimensional network structure formed by an aggregate of nanofibers. The nanofibers include quantum dots.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the national phase entry of InternationalApplication No. PCT/KR2016/007555, filed on Jul. 12, 2016, which claimspriority from the Korean patent application no. 10-2015-0099367 filed onJul. 13, 2015, and the Korean patent application no. 10-2015-0104501filed on Jul. 23, 2015, the entire contents of which are incorporatedherein by reference.

TECHNICAL FIELD

The present disclosure relates to an image display apparatus, and moreparticularly, to a quantum dot sheet having a fibrous-web structure fora quantum dot display, a method of manufacturing the same, and abacklight unit including the quantum dot sheet.

BACKGROUND

In general, a backlight unit (BLU) is a light source device disposedbehind a liquid crystal screen to emit light to the liquid crystalscreen such as a liquid crystal display (LCD), and uses light emittingdiodes (LEDs) as a light source. When LEDs are used as a light source,the backlight unit uses a red (R) or green (G) fluorescent material on ablue (B) LED chip to emit white light.

Recently, a backlight unit configured to emit white light using aquantum dot sheet 4 has been proposed (see FIG. 1). Since white lightrealized through the quantum dot sheet has excellent color expression incomparison to white light realized through existing blue LED chips andfluorescent materials, production of backlight units using the quantumdot sheet is gradually increasing.

Generally, as schematically shown in FIG. 1, a backlight unit thatadopts a quantum dot sheet includes a light guide plate 1, an LED lightsource 2 disposed on a side surface of the light guide plate 1, areflective plate 3 disposed under the light guide plate 1, and a quantumdot sheet 4, a diffusion sheet 5, and a prism sheet 6 sequentiallylaminated on the light guide plate, so that the backlight unit may emitwhite light.

For example, when the LED light source 2 is a B LED, the quantum dotsheet 4 including quantum dots configured to emit R and G light is used.Referring to FIG. 2, the quantum dot sheet 4 includes a quantum dotlayer 4 a in which quantum dots are distributed and barrier layers 4 bconfigured to cover upper and lower surfaces of the quantum dot layer 4a. The barrier layers 4 b block moisture and air from entering thequantum dot layer 4 a, and the quantum dot sheet 4 has a structure inwhich the barrier layers 4 b are adhered to the upper and lower surfacesof the quantum dot layer 4 a, and adhesive layers 4 c are additionallyprovided between the quantum dot layer 4 a and the barrier layers 4 b.The adhesive layer 4 c decreases light transmittance and lightefficiency, and a manufacturing process is complicated, and thusmanufacturing cost is increased.

In addition, in the quantum dot sheet 4, after the quantum dot layer 4 ais formed, the quantum dot layer 4 a comes into contact with air and isoxidized in a process of bonding the barrier layers 4 b to the upper andlower surfaces of the quantum dot layer 4 a, and the thickness of thequantum dot layer becomes thick, which makes it difficult to form thequantum dot sheet 4 into a slim structure, such that the volume and/or athickness of the backlight unit is increased.

Further, the existing quantum dot sheet 4 may have entangled oraggregated quantum dots in the quantum dot layer 4 a, such thatintrinsic properties of the quantum dots are degraded, and a defect oflight being unable to be uniformly emitted may frequently occur. Inorder to solve this problem, the quantum dot layer 4 a has to containmore quantum dots than a required reference value, which results inincreasing the manufacturing cost of the quantum dot sheet.

Therefore, it is necessary to develop a new quantum dot sheet in whichblue light can be converted into white light with high efficiency sothat the quantum dot sheet has superior color reproducibility and a slimstructure.

SUMMARY

The present disclosure is directed to providing a quantum dot sheethaving a fibrous-web structure, in which fibers including quantum dotsare formed into a web having a three-dimensional network structure, sothat white light may be realized with a small amount of quantum dots,and the quantum dot sheet may substitute for a diffusion sheet (or adiffusion film) in a backlight unit.

In addition, the present disclosure is directed to providing a method ofmanufacturing the quantum dot sheet having the fibrous-web structurewith high productivity.

Further, the present disclosure is directed to providing a backlightunit (BLU) having a reduced thickness, in which the quantum dot sheet isadopted to remove a diffusion sheet (or a diffusion film).

Moreover, the present disclosure is directed to providing a liquidcrystal display (LCD), a light emitting diode (LED) display, and an LEDlighting device having superior color reproducibility, in which the BLUis adopted.

According to one aspect of the present disclosure, a quantum dot sheethaving a fibrous-web structure includes a quantum dot layer having athree-dimensional network structure formed by an aggregate of nanofibersincluding quantum dots.

The quantum dot sheet having the fibrous-web structure may furtherinclude a fluorescent substance in the three-dimensional networkstructure.

The quantum dot sheet having the fibrous-web structure may have asingle-layer structure composed of a quantum dot layer.

The quantum dot sheet having the fibrous-web structure may furtherinclude a support layer or a barrier layer disposed downstream of thequantum dot layer when viewed from a light transmission direction.

The quantum dot sheet having the fibrous-web structure may furtherinclude a barrier layer disposed upstream of the quantum dot layer whenviewed from the light transmission direction.

The nanofibers may include: quantum dots; and a polymer resin, whereinthe nanofibers may include 1 to 6 parts by weight of the quantum dotsbased on 100 parts by weight of the polymer resin.

The quantum dot layer may be formed to have the three-dimensionalnetwork structure by forming an aggregate in which the nanofibers arelaminated by electrospinning or electrospraying a mixed solutionincluding the quantum dots and the polymer resin.

The quantum dot layer may include: quantum dots; a fluorescentsubstance; and a polymer resin, wherein the nanofibers may include 0.5to 5 parts by weight of the quantum dots based on 100 parts by weight ofthe polymer resin.

The quantum dot layer may include 10 to 20 parts by weight of thefluorescent substance based on 100 parts by weight of the polymer resin.

The quantum dot layer may be formed to have the three-dimensionalnetwork structure by forming an aggregate in which the nanofibers arelaminated by electrospinning or electrospraying a mixed solutionincluding the quantum dots, the fluorescent substance, and the polymerresin.

The quantum dots may include at least one type of quantum dot selectedfrom: a red-based quantum dot having a photoluminescence (PL) wavelengthpeak of 600 nm to 750 nm; a yellow-based quantum dot having a PLwavelength peak of 550 nm to 600 nm; and a green-based quantum dothaving a PL wavelength peak of 490 nm to 530 nm.

The quantum dot layer may include the red-based quantum dots and thegreen-based quantum dots in a weight ratio of 1:2 to 1:4.

The quantum dot layer may include the red-based quantum dots and theyellow-based quantum dots in a weight ratio of 1:0.8 to 1:2.5.

The fluorescent substance may include at least one selected from among asilicate-based fluorescent substance, a sulfide-based fluorescentsubstance, a nitrate-based fluorescent substance, a nitride-basedfluorescent substance, and an aluminate-based fluorescent substance.

The quantum dot layer may include the red-based quantum dots and thegreen-based quantum dots in a weight ratio of 1:10 to 1:40.

The nanofibers of the quantum dot layer may be coated with a barriermaterial.

The barrier layer may be formed upstream of the quantum dot layerthrough spray-coating or spin-coating.

The support layer and the barrier layer may include the same resin asthe polymer resin constituting the quantum dot layer, and the barrierlayer may be in the form of a sheet, a film, or a coating layer.

The nanofibers may have an average particle diameter of 200 nm to 1,000nm, the quantum dots may have an average particle diameter of 1 nm to 50nm, and the quantum dot layer may have an average thickness of 3 μm to100 μm.

The fluorescent substance may have an average particle diameter of 2,000nm to 30,000 nm.

In the quantum dot sheet having the fibrous-web structure, when a colorcoordinate of an area of 1.5 mmØ in the quantum dot sheet is measured byusing a color coordinate system measurement device under conditions inwhich a distance between a blue light source and the quantum dot sheetis 0.5 m and a measurement angle is 0.2°, a CIE x value and a CIE yvalue may satisfy color coordinate values of the following Expressions 1and 2:0.25≤CIE x≤0.35; and  [Expression 1]0.30≤CIE y≤0.40.  [Expression 2]

The quantum dot sheet having the fibrous-web structure may have a colorreproduction rate of 100% or more and a luminance of 4,600 cd/m² or moreon the basis of a 100% NTSC color gamut based on CIE 1931 colorcoordinates.

According to another aspect of the present disclosure, a method ofmanufacturing a quantum dot sheet having a fibrous-web structureincludes: a first step of preparing a mixed solution including a quantumdot dispersion solution containing quantum dots, a polymer resin, and asolvent; a second step of forming an aggregate in which nanofibers arelaminated by electrospinning or electrospraying the mixed solution on atop surface of a support layer or a barrier layer; and a third step ofdrying the aggregate in which the nanofibers are laminated to form aquantum dot layer having a three-dimensional network structure.

The mixed solution prepared in the first step may further include afluorescent sub stance.

The method of manufacturing the quantum dot sheet having the fibrous-webstructure may further include a fourth step of laminating a barrierlayer on one surface of the quantum dot layer.

The method of manufacturing the quantum dot sheet having the fibrous-webstructure may further include, after the third step or the fourth step,separating the quantum dot layer from the support layer formed under thequantum dot layer or from the barrier layer.

According to still another aspect of the present disclosure, a backlightunit includes various types of quantum dot sheets having the fibrous-webstructures as described above.

The backlight unit may not include a diffusion sheet (or a diffusionfilm) as a component, and may include a light guide plate, the quantumdot sheet, and a prism sheet.

The quantum dot sheet and the prism sheet may be sequentially laminatedon a top surface of the light guide plate.

The backlight unit may further include a reflective plate disposed on abottom surface of the light guide plate.

According to yet another aspect of the present disclosure, a lightemitting diode (LED) lighting device includes various types of quantumdot sheets having the fibrous-web structures as described above.

According to yet another aspect of the present disclosure, a displaydevice such as a liquid crystal display (LCD) and a light emitting diode(LED) includes the backlight unit.

According to the present disclosure, there is provided a web-typequantum dot sheet in which a fibrous aggregate has a three-dimensionalnetwork structure, different from a conventional plate-type quantum dotsheet, in which light is diffuse-reflected because of a structure and aform of the web-type quantum dot sheet, so that a volume and/or athickness of a backlight unit (BLU) can be reduced by omitting theapplication of a diffusion sheet during manufacture of the BLU, quantumdots can be uniformly dispersed, degradation of the quantum dots can bedecreased, it is possible to emit white light through the BLU whileusing less quantum dots than those of a conventional quantum dot sheet,and high color reproducibility can be implemented. In addition, sincethe quantum dot sheet of the present disclosure has the fibrous-webstructure, the quantum dot sheet has excellent in flexibility, such thatthe quantum dot sheet can be applied to a flexible display, a flexiblelighting device, or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view illustrating a backlight unit thatadopts a conventional quantum dot sheet.

FIG. 2 is a schematic sectional view illustrating the conventionalquantum dot sheet.

FIG. 3 is a sectional view schematically illustrating a quantum dotsheet according to one embodiment of the present disclosure.

FIG. 4 is a schematic enlarged view illustrating nanofibers forming athree-dimensional network structure in the quantum dot sheet.

FIG. 5 is a schematic enlarged view illustrating the nanofibers formingthe three-dimensional network structure in the quantum dot sheet and thequantum dot sheet in which a fluorescent substance is fixed by ananofiber aggregate.

FIG. 6 is a sectional view schematically illustrating a quantum dotsheet according to another embodiment of the present disclosure.

FIG. 7 is a sectional view schematically illustrating a quantum dotsheet according to still another embodiment of the present disclosure.

FIG. 8 is a schematic sectional view illustrating a backlight unit thatadopts the quantum dot sheet of the present disclosure.

FIG. 9 illustrates a CIE 1931 color coordinate system.

Description of Reference numerals: 1: Light guide plate 2: Light (orLight guide sheet) source 3: Reflective plate 5: Diffusion sheet 6:Prism sheet 11: Quantum dot layer 13: Fluorescent substance 15: Quantumdot 17: Support layer 19: Barrier layer 4, 100: Quantum dot sheet

DETAILED DESCRIPTION OF THE INVENTION

The term “layer” or “sheet” used herein is meant to include all forms ofa sheet, a film, and a plate unless described otherwise.

Hereinafter, exemplary embodiments of the present disclosure will bedescribed in detail with reference to the accompanying drawings suchthat those skilled in the art may easily implement the embodiments. Thepresent disclosure may be implemented in various forms, but is notlimited to the exemplary embodiments described herein. In the drawings,portions irrelevant to the description will not be shown in order tomake the present disclosure clear, and same reference numerals refer tosame or like elements throughout the specification.

Referring to FIG. 3, according to one exemplary embodiment of thepresent disclosure, a quantum dot sheet 100 has a nano-fibrous aggregatehaving a three-dimensional network structure.

In addition, as shown in FIG. 4, nanofibers constituting the quantum dotsheet 100 include quantum dots 15, and the quantum dot sheet of thepresent disclosure has a fibrous-web structure in which the quantum dotsmay be uniformly dispersed, and degradation of the quantum dots may bedecreased.

Referring to FIG. 5, the nanofibers constituting the quantum dot sheet100 include the quantum dots 15, a fluorescent substance 13 is containedin the three-dimensional network structure formed by the nanofiberaggregate, and the fluorescent substance is fixed by the nanofiberaggregate, so that the fluorescent substance may be disposed inside thethree-dimensional network structure.

Referring to FIG. 6, when viewed from a light transmission (ortraveling) direction, the quantum dot sheet 100 may be formed bylaminating a quantum dot layer 11 on one surface of a support layer 17or a barrier layer, or the quantum dot sheet of the present disclosuremay be peeled off from the support layer or the barrier layer such thatthe quantum dot sheet is formed only by the quantum dot layer (see FIG.3). The quantum dot layer may have nanofibers densely formed so as tohave no air gaps when viewed from the top.

In addition, referring to FIG. 7, the quantum dot sheet 100 may beformed by laminating the barrier layer 19 on one or both surfaces of thequantum dot layer 11 to prevent the quantum dots in the nanofibers frombeing oxidized, or a surface of the nanofibers constituting the quantumdot layer may be coated with a barrier material to prevent the quantumdots from being oxidized.

When light passes through the quantum dot sheet 100 of the presentdisclosure, the light is diffuse-reflected by the nanofibersconstituting the quantum dot sheet, which provides a light diffusioneffect, so that the quantum dot sheet may serve as a diffusion sheet,and thus a BLU without a diffusion sheet may be provided asschematically shown in FIG. 8. That is, a BLU in which the quantum dotsheet and the prism sheet are sequentially laminated on a top surface ofa light guide plate may be provided. In addition, a reflective plate maybe disposed on a bottom surface of the light guide plate of the BLU.

The present disclosure will be described in more detail through adescription of a method of manufacturing a quantum dot sheet.

The quantum dot sheet of the present disclosure may be manufactured byperforming: a first step of preparing a mixed solution including aquantum dot dispersion solution containing quantum dots, a polymerresin, and a solvent; a second step of forming an aggregate in whichnanofibers are laminated by electrospinning or electrospraying the mixedsolution; and a third step of heat-curing the aggregate in which thenanofibers are laminated to form a quantum dot layer having athree-dimensional network structure.

In addition, a fluorescent substance may be added into the mixedsolution to form a quantum dot layer as shown in FIG. 5.

The quantum dot of the quantum dot dispersion solution is a particle inwhich a nano-sized II-IV group semiconductor particle serves as a core,and the fluorescence of the quantum dot is light generated whenelectrons, which are in an excited state, are transitioned from aconduction band to a valence band. In the present disclosure, thequantum dots may include at least one type of quantum dot selected from:a red-based quantum dot having a photoluminescence (PL) wavelength peakof 600 nm to 750 nm; a yellow-based quantum dot having a PL wavelengthpeak of 550 nm to 600 nm; and a green-based quantum dot having a PLwavelength peak of 490 nm to 530 nm, and preferably include at least twotypes of quantum dots selected from the same. More preferably, thered-based quantum dots and the green-based quantum dots may be mixed ina weight ratio of 1:2 to 1:4 to realize white light, or the red-basedquantum dots and the yellow-based quantum dots may be mixed in a weightratio of 1:0.8 to 1:2.5 to realize white light.

In addition, the quantum dots may be those generally used in the art. Indetail, the quantum dots include II-VI group, III-V group, IV-VI groupand IV group semiconductors, and the quantum dots in the presentdisclosure may include at least one selected from Si, Ge, Sn, Se, Te, B,C, P, BN, BP, BAs, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP,InAs, InSb, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, ZnO, ZnS, ZnSe,ZnTe, CdS, CdSe, Cd_(x)Se_(y)S_(z), CdTe, HgS, HgSe, HgTe, BeS, BeSe,BeTe, MgS, MgSe, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbO, PbS, PbSe, PbTe,CuF, CuCl, CuInS₂, Cu₂SnS₃, CuBr, CuI, Si₃N₄, Ge₃N₄, Al₂O₃, (Al, Ga,In)₂(S, Se, Te)₃, CIGS, CGS, and (ZnS)_(y)(Cu_(x)Sn_(1-x)S₂)_(1-y),wherein 0<x<1, and y is a rational number satisfying 0<y<1. Further, thequantum dots may have a core/shell structure or an alloy structure.Non-limiting examples of quantum dots having the core/shell structure orthe alloy structure include CdSe/ZnS, CdSe/ZnSe/ZnS,CdSe/CdS_(x)(Zn_(1-y)Cd_(y))S/ZnS, CdSe/CdS/ZnCdS/ZnS, InP/ZnS,InP/Ga/ZnS, InP/ZnSe/ZnS, PbSe/PbS, CdSe/CdS, CdSe/CdS/ZnS, CdTe/CdS,CdTe/ZnS, CuInS2/ZnS, Cu2SnS3/ZnS, etc. Specific examples of the quantumdots are described for the purpose of comprehension of the presentdisclosure, and the present disclosure is not limited to the above typesof quantum dots.

In addition, the quantum dots have an average particle diameter of 1 nmto 50 nm, preferably 2 nm to 30 nm, and more preferably 2 nm to 20 nm.In this case, when the average particle diameter of the quantum dotsexceeds 50 nm, quantum dots separated from the nanofibers may increasein number during electrospinning or electrospraying, so it is preferableto use quantum dots having an average particle diameter within the aboverange.

As a specific example, the red-based quantum dots are CdSe having anaverage particle diameter of 5.2 nm to 8 nm, and the green-based quantumdots are CdSe having an average particle diameter of 3 nm to 4.5 nm, andthe red-based quantum dots and the green-based quantum dots may be mixedfor use.

As another specific example, the red-based quantum dots are CuInS₂having an average particle diameter of 4.5 nm to 5.2 nm, and theyellow-based quantum dots are CuInS₂ having an average particle diameterof 2.5 nm to 4.0 nm, and the red-based quantum dots and the yellow-basedquantum dots may be mixed for use.

In addition, the quantum dot dispersion solution includes a solvent foruniform dispersion. For example, the solvent of the quantum dotdispersion solution may include one or two selected from toluene,formamide, dimethylsulfoxide, dimethylformamide, acetic acid,acetonitrile, methoxyethanol, tetrahydrofuran, benzene, xylene,cyclohexane, methanol, chloroform, and acetone.

Further, when a quantum dot layer as shown in FIG. 4 is formed, anamount of the quantum dots in the mixed solution may be 1 to 6 parts byweight, preferably 2 to 4 parts by weight based on 100 parts by weightof the polymer resin. In this case, it may be difficult to realize whitelight when the amount of the quantum dots is less than 1 part by weight,and it is uneconomical for the quantum dots to exceed 6 parts by weight,so it is preferable for the quantum dots to fall within the above range.

In addition, when a quantum dot layer shown in FIG. 5 is formed, theamount of the quantum dots in the mixed solution may be in the range of0.5 to 5 parts by weight, preferably 0.8 to 3 parts by weight based on100 parts by weight of the polymer resin. In this case, the amount ofthe fluorescent substance has to be increased to realize white light,and the color reproduction rate may be reduced when the amount of thequantum dots is less than 0.5 parts by weight. It is uneconomical forthe quantum dots to exceed 5 parts by weight, so it is preferable forthe quantum dots to fall within the above range.

The fluorescent substance may be a fluorescent substance generally usedin the art, preferably one or at least two selected from among asilicate-based fluorescent substance, a sulfide-based fluorescentsubstance, a nitrate-based fluorescent substance, a nitride-basedfluorescent substance, and an aluminate-based fluorescent substance.

For example, the fluorescent substance may be one or at least twoselected from among (Sr, Ca)B₄O₇:Eu, BaMgAl₁₀O₁₇:Eu, Y₂O₃:Eu, InBO₃:Eu,YVO₄:Eu, YBO₃:Eu, (Y, Gd)BO₃:Eu, SrTiO₃:Eu, (Si, Al)₆(O, N)₈:Eu,Y₂O₂S:Eu, La₂O₂S:Eu, (La, Mn, Sm)₂O₂S.Ga₂O₃:Eu, (Ca, Sr)S:Eu,CaAlSiN₃:Eu, (Sr, Ca)AlSiN₃:Eu, Sr₂Si₅N₈:Eu, CaGa₂S₄:Eu, SrGa₂S₄:Eu,SrSi₂O₂N₂:Eu, BaGa₂S₄:Eu, SrAl₂O₄:Eu, BAM:Eu, (Ba, Sr, Ca)₂SiO₄:Eu, (Sr,Ba, Ca, Mg, Zn)₂Si(OD)₄:Eu (wherein D is F, Cl, S, N, or Br),β-SiAlON:Eu, Ba₃Si₆O₁₂N₂:Eu, Ba₂MgSi₂O₇:Eu, Mg₂SiO₄:Mn, Zn₃(PO₄)₂:Mn,(Y, Gd)BO₃:Tb, Ca₃(Sc, Mg)₂Si₃O₁₂:Ce, Y₂SiO₅:Ce, Ca₃Y₂Si₆O₈:Ce,BaAl₁₂O₁₉:Mn, Y₃Al₅O₁₂:Ce, Y₃Al₅O₁₂:Tb, Zn₂SiO₄:Mn, InBO₃:Tb, ZnS:Cu,and Ca₁₀(PO₄)₆Cl₂. Preferably, the red-based fluorescent substance mayinclude at least one selected from among Y₂O₂S:Eu, La₂O₂S:Eu, (La, Mn,Sm)₂O₂S.Ga₂O₃:Eu, (Ca, Sr)S:Eu, CaAlSiN₃:Eu, (Sr, Ca)AlSiN₃:Eu, andSr₂Si₅N₈:Eu, and the green-based fluorescent substance may include atleast one selected from among CaGa₂S₄:Eu, SrGa₂S₄:Eu, SrSi₂O₂N₂:Eu,BaGa₂S₄:Eu, SrAl₂O₄:Eu, BAM:Eu, (Ba, Sr, Ca)₂SiO₄:Eu, (Sr, Ba, Ca, Mg,Zn)₂Si(OD)₄:Eu (wherein D is F, Cl, S, N, or Br), β-SiAlON:Eu,Ba₃Si₆O₁₂N₂:Eu, Ba₂MgSi₂O₇:Eu, and Ca₃(Sc, Mg)₂Si₃O₁₂:Ce.

In addition, the fluorescent substance has an average particle diameterof 2,000 nm to 30,000 nm, preferably 5,000 nm to 25,000 nm, and morepreferably 6,000 nm to 16,000 nm. In this case, when the averageparticle diameter of the fluorescent substance exceeds 30,000 nm, sincethe particle diameter is too large, it is difficult for the fluorescentsubstance to be fixed by the nanofibers after the electrospinning orelectrospraying, such that the fluorescent substance may be separatedfrom the quantum dot layer, so it is preferable to use a fluorescentsubstance having an average particle diameter within the above range.

In this case, an amount of the fluorescent substance may be in the rangeof 10 to 20 parts by weight, preferably 12 to 18 parts by weight basedon 100 parts by weight of the polymer resin. In this case, a wavelengthmay be insufficient to realize white light when the amount of thefluorescent substance is less than 10 parts by weight, anddispersibility may be decreased when the amount of the fluorescentsubstance exceeds 20 parts by weight.

In addition, the quantum dots and the fluorescent substance are adjustedto be in a weight ratio of 1:10 to 1:40, preferably 1:10 to 1:25, andmore preferably 1:12 to 1:20 by weight, which is advantageous in termsof ensuring high color reproducibility. For example, the quantum dotsmay be the red-based quantum dots, and the fluorescent substance may beat least one selected from the green-based fluorescent substance and theyellow-based fluorescent substance.

Alternatively, the quantum dots may be at least one selected from thegreen-based quantum dots and the yellow-based quantum dots, and thefluorescent substance may be the red-based fluorescent substance.

The polymer resin prepared in the first step may include one or amixture of at least two selected from among polyethyleneterephthalateresin, polycarbonate resin, polyalkylmethacrylate resin,polymethacrylate resin, polyvinylidene fluoride resin, polystyreneresin, polyvinyl chloride resin, styrene acrylonitrile copolymer resin,polyurethane resin, polyamide resin, polyvinyl butyral resin, siliconeresin, polyvinyl acetate resin, and unsaturated polyester resin.Preferably, the polymer resin prepared in the first step may include oneor a mixture of at least two selected from amongpolyethyleneterephthalate resin, polycarbonate resin,polyalkylmethacrylate resin, and polyvinylidene fluoride resin havingexcellent transparency. For example, polyalkylmethacrylate resin andpolyvinylidene fluoride resin may be mixed in a weight ratio of 5 to 7:3to 5.

The solvent of the mixed solution prepared in the first step dissolvesthe polymer resin, and may be a solvent generally used in the art. Anamount of the solvent is 500 to 20,000 parts by weight, preferably 600to 5,000 parts by weight, and more preferably 650 to 1,500 parts byweight based on 100 parts by weight of the polymer resin, which ispreferable in terms of maintaining a viscosity appropriate forelectrospinning or electrospraying the mixed solution. The solvent ofthe mixed solution may be one or a mixture of at least two selected fromamong dim ethyl sulfoxide, dimethylformamide, dimethylacetamide,acetone, toluene, formamide, acetic acid, acetonitrile, methoxyethanol,tetrahydrofuran, benzene, xylene, and cyclohexane.

The second step is forming the nanofibers and the aggregate of thenanofibers by electrospinning or electrospraying the mixed solutionprepared in the first step. In the forming of the nanofibers and theaggregate of the nanofibers, electrospinning is preferred when the mixedsolution has a high concentration (high viscosity), and electrosprayingis preferred when the mixed solution has a low concentration (lowviscosity).

In the second step, a two-layer structure (support layer-quantum dotlayer or barrier layer-quantum dot layer) may be formed byelectrospinning or electrospraying the mixed solution on a top surfaceof the support layer or the barrier layer. In this case, the supportlayer or the barrier layer may be formed of one or a mixture of at leasttwo selected from among polyethyleneterephthalate resin, polycarbonateresin, polyalkylmethacrylate resin, polymethacrylate resin,polyvinylidene fluoride resin, polystyrene resin, polyvinyl chlorideresin, styrene acrylonitrile copolymer resin, polyurethane resin,polyamide resin, polyvinyl butyral resin, silicone resin, polyvinylacetate resin, and unsaturated polyester resin. Preferably, the supportlayer or the barrier layer may be formed of one or a mixture of at leasttwo selected from polyethyleneterephthalate resin, polycarbonate resin,polyalkylmethacrylate resin, polymethacrylate resin, and polyvinylidenefluoride resin. When the quantum dot sheet has a structure including twolayers or more, bonding strength with the quantum dot layer may beimproved by using the same polymer resin as the mixed solution.

Electrospinning or electrospraying is performed in the second step suchthat the nanofiber has an average particle diameter of 200 nm to 1,000nm, preferably 200 nm to 800 nm, and more preferably 250 nm to 600 nm.Here, there may be a problem in shape stability and the quantum dots mayprotrude when the average particle diameter of the nanofibers is 200 nm,which is too small. When the average particle diameter exceeds 1,000 nm,a diffuse reflection effect of light may be reduced.

In addition, to form the aggregate of laminated nanofibers having abarrier coating layer, a barrier material may be spin-coated orspray-coated on a surface of the nanofibers formed by theelectrospinning or electrospraying in the second step.

The third step is drying the aggregate of nanofibers laminated in thesecond step to form the quantum dot layer having the three-dimensionalnetwork structure. The quantum dot layer may have an average thicknessof 3 μm to 100 μm, preferably 3 μm to 60 μm, and more preferably 3 μm to50 μm.

In addition, drying is performed to remove the remaining solvent andadditionally enhance adhesion in a bonding region between thenanofibers. A drying temperature may be variously selected based on thetypes of the solvent and the polymer resin, and it is preferred toperform the drying using a method such as hot air drying by applyingheat having a temperature of 30° C. to 60° C.

Further, the method of manufacturing the quantum dot sheet may furtherinclude a fourth step of laminating the barrier layer on one surface ofthe quantum dot layer.

In this case, the barrier layer formed in the fourth step may be formedof one or a mixture of at least two selected from polycarbonate resin,polymethacrylate resin, and polyvinylidene fluoride resin, preferablythe same resin as the polymer resin prepared in the first step toimprove the bonding strength between the quantum dot layer and thebarrier film (or a coating layer).

In addition, a step of separating the quantum dot layer from the supportlayer formed at a bottom of the quantum dot layer is performed after thethird step or the fourth step to manufacture a quantum dot sheet havinga single-layer structure including only the quantum dot layer as shownin FIG. 3, or to manufacture a quantum dot sheet having a two-layerstructure in which a barrier layer is laminated on one surface of thequantum dot layer.

In the above quantum dot sheet having the fibrous-web structureaccording to the present disclosure, when a color coordinate of an areaof 1.5 mmØ in the quantum dot sheet is measured (see CIE 1931 colorcoordinates in FIG. 9) using a color coordinate system measurementdevice under conditions in which a distance between a blue light sourceand the quantum dot sheet is 0.5 m and a measurement angle is 0.2°, aCIE x value and a CIE y value may satisfy color coordinate values of thefollowing Expressions 1 and 2:0.23≤CIE x≤0.37, preferably 0.25≤CIE x≤0.35, and more preferably0.26≤CIE x≤0.32; and  [Expression 1]0.28≤CIE y≤0.42, preferably 0.30≤CIE y≤0.40, and more preferably0.30≤CIE y≤0.37.  [Expression 2]

In addition, according to the present disclosure, the quantum dot sheetas shown in FIG. 4 has a high color reproduction rate of 100% or more,preferably 105% or more on the basis of a 100% NTSC color gamut based onCIE 1931 color coordinates, so that the quantum dot sheet may havesuperior color reproducibility. Further, the quantum dot sheet may havea high luminance of 5,200 cd/m² or more, preferably 5,500 cd/m² or more.

Moreover, according to the present disclosure, when the quantum dots andthe fluorescent substances are adopted as shown in FIG. 5, the quantumdot sheet has a high color reproduction rate of 100% or more, preferably102% or more, and more preferably 103% or more on the basis of the 100%NTSC color gamut based on the CIE 1931 color coordinates, so that thequantum dot sheet may have superior color reproducibility. In addition,the quantum dot sheet may have a high luminance of 4,600 cd/m² or more,preferably 4,800 cd/m² or more, and more preferably 4,850 cd/m² to 6,000cd/m².

Hereinafter, the present disclosure will be described in more detailbased on examples. However, the following examples are described for thepurpose of comprehension of the present disclosure, and should not beconstrued as limiting the scope of the present disclosure by thefollowing examples.

EXAMPLES Preparation Example 1-1: Preparation of Red-Based Quantum DotDispersion Solution

A quantum dot dispersion solution of CdSe having a PL wavelength peak of650 nm to 660 nm and an average particle diameter of 5.8 nm to 6.1 nmdispersed in a toluene solvent was prepared.

Preparation Example 1-2: Preparation of Red-Based Quantum Dot DispersionSolution

A quantum dot dispersion solution of CuInS₂ having a PL wavelength peakof 695 nm to 710 nm and an average particle diameter of 4.8 nm to 5.0 nmdispersed in an acetone solvent was prepared.

Preparation Example 2-1: Preparation of Green-Based Quantum Dot

A quantum dot dispersion solution of CdSe having a PL wavelength peak of505 nm to 510 nm and an average particle diameter of 3.9 nm to 4.1 nmdispersed in a toluene solvent was prepared.

Preparation Example 2-2: Preparation of Yellow-based Quantum Dot

A quantum dot dispersion solution of CuInS₂ having a PL wavelength peakof 550 nm to 560 nm and an average particle diameter of 2.8 nm to 3.0 nmdispersed in an acetone solvent was prepared.

Preparation Example 3: Preparation of Green-Based Fluorescent Substance

A Ba₂MgSi₂O₇:Eu fluorescent powder having an average particle diameterof 8,215 nm was prepared.

Example 1-1

A polymer resin containing a polyvinylidene fluoride (PVDF) resin and apolymethyl methacrylate (PMMA) resin in a weight ratio of 6:4, thequantum dot dispersion solution prepared in Preparation Example 1-1 andPreparation Example 2-1, and a dimethylacetamide solvent were mixed andagitated to prepare a mixed solution.

In this case, the mixing ratio was 1.2 parts by weight of red-basedquantum dots in the red-based dispersion solution, 2.8 parts by weightof green-based quantum dots in the green-based dispersion solution, and934 parts by weight of the solvent based on 100 parts by weight of thepolymer resin.

The mixed solution was electrospun on a PET film, which was a support,and dried with hot air at 45° C. to 48° C. to form a quantum dot layerhaving an average thickness of 24 μm.

Next, the quantum dot layer was peeled off from the PET film, which wasthe support, to manufacture the quantum dot sheet having the fibrous-webstructure including a single layer as shown in FIG. 3.

At this time, the average particle diameter of the nanofibersconstituting the quantum dot layer of the quantum dot sheet was in therange of 290 nm to 300 nm.

Experimental Example 1: Measurement of Color Coordinates, ColorReproduction Rate, and Luminance

The quantum dot sheet formed in Example 1-1 was used to measure a colorcoordinate of an area of 1.5 mmØ in the quantum dot sheet, colorreproduction rate, and luminance on the basis of a 100% NTSC color gamut(based on CIE 1931 color coordinates; see FIG. 9) by using a colorcoordinate system measurement device (BM-7 of Topcon) under conditionsin which a distance between a blue light source (having intensity of 500W) and the quantum dot sheet was 0.5 m, and a measurement angle was0.2°. In order to increase the accuracy of measurement results, theanalysis was performed five times, and an average value was calculated.The results are shown in Table 1 below.

TABLE 1 Color Color coordinates reproduction Luminance ClassificationCIE x CIE y rate (cd/m²) First time 0.2702 0.3002 105.8% 5,635 Secondtime 0.2710 0.3011 106.5% 5,692 Third time 0.2700 0.3004 106.3% 5,595Fourth time 0.2694 0.3004 105.0% 5,709 Fifth time 0.2711 0.3006 105.6%5,684 Average 0.2703 0.3006 105.8% 5,663

Referring to the experimental results shown in Table 1, according to thepresent disclosure, the quantum dot sheet including only the quantum dotlayer of Example 1-1 had color coordinates of CIE x=0.2703, and CIEy=0.3006, and it was found that the blue light source realized whitelight through the CIE 1931 color coordinates shown in FIG. 9. Inaddition, it was found that the quantum dot sheet had a very high colorreproduction rate of 105.8% and a high luminance of 5,500 cd/m² or more.

Example 1-2

The polymer resin containing the PVDF resin and the PMMA resin in theweight ratio of 6:4, the quantum dot dispersion solution prepared inPreparation Example 1-2 and Preparation Example 2-2, and thedimethylacetamide solvent were mixed and agitated to prepare a mixedsolution.

In this case, the mixing ratio was 1.4 parts by weight of red-basedquantum dots in the red-based dispersion solution, 1.75 parts by weightof yellow-based quantum dots in the yellow-based dispersion solution,and 932 parts by weight of the solvent based on 100 parts by weight ofthe polymer resin.

The mixed solution was electrospun on a PET film, which was the support,and dried with hot air at 45° C. to 48° C. to form a quantum dot layerhaving an average thickness of 22 μm to 23 μm.

Next, the quantum dot layer was peeled off from the PET film, which wasthe support, to manufacture the quantum dot sheet having the fibrous-webstructure including a single layer as shown in FIG. 3.

At this time, the average particle diameter of the nanofibersconstituting the quantum dot layer of the quantum dot sheet was in therange of 275 nm to 285 nm.

Example 1-3

A quantum dot sheet having the fibrous-web structure including a singlelayer was manufactured in the same manner as in Example 1-2, except thatthe average thickness of the quantum dot layer was in the range of 46 μmto 48 μm.

Example 1-4

A quantum dot sheet having the fibrous-web structure including a singlelayer was manufactured in the same manner as in Example 1-2, except thatthe average thickness of the quantum dot layer was in the range of 46 μmto 48 μm. Here, the average particle diameter of the nanofibersconstituting the quantum dot layer of the quantum dot sheet was in therange of 560 nm to 570 nm.

Comparative Example 1-1: Manufacture of Quantum Dot Sheet

The polymer resin containing the PVDF resin and the PMMA resin in theweight ratio of 6:4, the quantum dot dispersion solution prepared inPreparation Example 1-2 and Preparation Example 2-2, and thedimethylacetamide solvent were mixed and agitated to prepare a mixedsolution.

In this case, the mixing ratio was 1.4 parts by weight of red-basedquantum dots in the red-based dispersion solution, 1.8 parts by weightof yellow-based quantum dots in the yellow-based dispersion solution,and 820 parts by weight of the solvent based on 100 parts by weight ofthe polymer resin.

The mixed solution was comma-coated on a PET film, which was thesupport, and dried with hot air at 70° C. to 72° C. to form a quantumdot layer having a film form and an average thickness of 22.6 μm.

Next, the quantum dot layer was peeled off from the PET film, which wasthe support, to manufacture a sheet-type quantum dot sheet.

Comparative Example 1-2

A quantum dot sheet having the fibrous-web structure including a singlelayer was manufactured in the same manner as in Example 1-4, except thatthe average thickness of the quantum dot layer was 46 μm to 48 μm. Here,the average particle diameter of the nanofibers constituting the quantumdot layer of the quantum dot sheet was in the range of 1,072 nm to 1,075nm.

Comparative Example 1-3

A quantum dot sheet (having an average thickness of 22 μm to 23 μm)having the fibrous-web structure including a single layer was formed inthe same manner as in Example 1-2, except that a mixed solution(spinning solution) used for the electrospinning was prepared so as toinclude 3.2 parts by weight of red-based quantum dots in the red-baseddispersion solution, 4.2 parts by weight of yellow-based quantum dots inthe yellow-based dispersion solution, and 932 parts by weight of thesolvent based on 100 parts by weight of the polymer resin, and used tomanufacture the quantum dot sheet.

Comparative Example 1-4

A quantum dot sheet (having an average thickness of 22 μm to 23 μm)having the fibrous-web structure including a single layer was preparedin the same manner as in Example 1-2, except that a mixed solution(spinning solution) used for the electrospinning was prepared so as toinclude 0.8 parts by weight of red-based quantum dots in the red-baseddispersion solution, 3 parts by weight of yellow-based quantum dots inthe yellow-based dispersion solution, and 932 parts by weight of thesolvent based on 100 parts by weight of the polymer resin, and used tomanufacture the quantum dot sheet.

Experimental Example 2: Measurement of Color Coordinates, ColorReproduction Rate, and Luminance

The color coordinate, the color reproduction rate, and the luminancewere measured in the same manner as in Experimental Example 1 using thequantum dot sheets formed in Examples 1-2 to 1-4 and ComparativeExamples 1-1 to 1-4, and the results are shown in Table 2 below. At thistime, each measurement value represents an average value obtained aftermeasuring five times.

TABLE 2 Color Color coordinates reproduction Luminance ClassificationCIE x CIE y rate (cd/m²) Example 1-2 0.2842 0.3327 105.2% 5,574 Example1-3 0.2819 0.3253 105.4% 5,626 Example 1-4 0.2822 0.3246 105.3% 5,637Comparative 0.3053 0.3489  99.4% 5,026 Example 1-1 Comparative 0.29070.3280 104.7% 5,191 Example 1-2 Comparative 0.2801 0.3358 105.4% 5,595Example 1-3 Comparative 0.3523 0.3967 103.2% 5,426 Example 1-4

In Examples 1-2 to 1-4, it was found that the color coordinatessatisfied 0.26≤CIE x≤0.32 and 0.30≤CIE y≤0.37 to realize white light,and the color reproduction rate was 105% or more. In particular, thecolor reproduction rate of non-cadmium-based quantum dots tended to beslightly lower than the color reproduction rate of cadmium-based quantumdots. Comparing the color reproduction rates of Comparative Example 1-1of a coating film (or a film membrane) with Example 1-2, it was foundthat the quantum dot sheet manufactured to have the fibrous-webstructure obtained an effect of enhanced color reproduction rate.

In the case of Comparative Example 1-2 in which the average particlediameter of the nanofibers exceeded 1,000 nm, when compared with Example1-4, there was no significant influence on the color coordinates and thecolor reproduction rate, whereas the luminance significantly decreasedto less than 5,200 cd/m², and it was determined that the luminancedecreased because the diffuse reflection effect of light decreased.

In the case of Comparative Example 1-3 in which more than 6 parts byweight of quantum dots were used based on 100 parts by weight of thepolymer resin, when compared with Example 1-2, there was almost nodifference in the color reproduction rate and a luminance enhancementeffect, and thus it was found that a large number of quantum dots isunnecessary.

In the case of Comparative Example 1-4 in which more than 2.5 weightparts of the yellow-based quantum dots were used relative to thered-based quantum dots, a CIE x value exceeded 0.32 and a CIE y valueexceeded 0.37, which made it difficult to realize white light, such thatthe color reproduction rate and the luminance tended to be lower whencompared with Example 2.

Example 2-1

The polymer resin containing the PVDF resin and the PMMA resin in theweight ratio of 6:4, the quantum dot dispersion solution prepared inPreparation Example 1-1, a fluorescent substance prepared in PreparationExample 3, and the dimethylacetamide solvent were mixed and agitated toprepare a mixed solution.

In this case, the mixing ratio was 1 part by weight of red-based quantumdots in the red-based dispersion solution, 15 parts by weight of thegreen-based fluorescent substance, and 960 parts by weight of thesolvent based on 100 parts by weight of the polymer resin.

The mixed solution was electrospun on a PET film, which was the support,and dried with hot air at 45° C. to 48° C. to form a quantum dot layerhaving an average thickness of 72 μm to 73 μm.

Next, the quantum dot layer was peeled off from the PET film, which wasthe support, to manufacture the quantum dot sheet having the fibrous-webstructure including a single layer as shown in FIGS. 3 and 4.

At this time, the average particle diameter of the nanofibersconstituting the quantum dot layer of the quantum dot sheet was 295 nmto 300 nm.

Experimental Example 3: Measurement of Color Coordinates, ColorReproduction Rate, and Luminance

The color coordinate, the color reproduction rate, and the luminancewere measured in the same manner as in Experimental Example 1 using thequantum dot sheet formed in Example 2-1, and the results are shown inTable 3 below. At this time, each measurement value represents anaverage value obtained after measuring five times.

TABLE 3 Color Color coordinates reproduction Luminance ClassificationCIE x CIE y rate (cd/m²) First time 0.2671 0.3088 102.5% 4,866 Secondtime 0.2680 0.3091 102.6% 4,890 Third time 0.2689 0.3094 102.7% 4,904Fourth time 0.2678 0.3093 102.5% 4,870 Fifth time 0.2689 0.3095 102.6%4,870 Average 0.2681 0.3092 102.6% 4,880

Referring to the experimental results shown in Table 3, according to thepresent disclosure, the quantum dot sheet including only the quantum dotlayer of Example 2-1 had color coordinates of CIE x=0.2681, and CIEy=0.3092, and it was found that the blue light source realized whitelight through the CIE 1931 color coordinates shown in FIG. 9. Inaddition, it was found that the quantum dot sheet had a very high colorreproduction rate of 102.6%, and a high luminance of 4,800 cd/m² ormore.

Example 2-2

The polymer resin containing the PVDF resin and the PMMA resin in theweight ratio of 6:4, the quantum dot dispersion solution prepared inPreparation Example 1-2, the fluorescent substance prepared inPreparation Example 3, and the dimethylacetamide solvent were mixed andagitated to prepare a mixed solution.

In this case, the mixing ratio was 1.2 parts by weight of red-basedquantum dots in the red-based dispersion solution, 15 parts by weight ofthe green-based fluorescent substance, and 960 parts by weight of thesolvent based on 100 parts by weight of the polymer resin.

The mixed solution was electrospun on a PET film, which was the support,and dried with hot air at 45° C. to 48° C. to form a quantum dot layerhaving an average thickness of 86 μm to 87 μm.

Next, the quantum dot layer was peeled off from the PET film, which wasthe support, to manufacture the quantum dot sheet having the fibrous-webstructure including a single layer as shown in FIGS. 3 and 4.

At this time, the average particle diameter of the nanofibersconstituting the quantum dot layer of the quantum dot sheet was in therange of 285 nm to 290 nm.

Example 2-3

A quantum dot sheet was manufactured in the same manner as in Example2-2, except that the mixed solution was prepared so as to include 1.2parts by weight of red-based quantum dots in the red-based dispersionsolution, 20 parts by weight of the green-based fluorescent substance,and 960 parts by weight of the solvent based on 100 parts by weight ofthe polymer resin.

Example 2-4

A quantum dot sheet was manufactured in the same manner as in Example2-2, except that the mixed solution was prepared so as to include 1.2parts by weight of red-based quantum dots in the red-based dispersionsolution, 30 parts by weight of the green-based fluorescent substance,and 960 parts by weight of the solvent based on 100 parts by weight ofthe polymer resin.

Example 2-5

A quantum dot sheet having the fibrous-web structure including a singlelayer was manufactured in the same manner as in Example 2-2, except thatthe average thickness of the quantum dot layer was 89 μm to 90 μm. Atthis time, the average particle diameter of the nanofibers constitutingthe quantum dot layer of the quantum dot sheet was in the range of 585nm to 595 nm.

Comparative Example 2-1

The mixed solution prepared in Example 2-2 was comma-coated on a PETfilm, which was the support, and dried with hot air at 70° C. to 72° C.to form a quantum dot layer having a film form and an average thicknessof 22.6 μm.

Next, the quantum dot layer was peeled off from the PET film, which wasthe support, to manufacture a sheet-type quantum dot sheet.

Comparative Example 2-2

A quantum dot sheet was manufactured in the same manner as in Example2-2, except that the mixed solution was prepared so as to include 1.2parts by weight of red-based quantum dots in the red-based dispersionsolution, 45 parts by weight of the green-based fluorescent substance,and 960 parts by weight of the solvent based on 100 parts by weight ofthe polymer resin.

Comparative Example 2-3

A quantum dot sheet was manufactured in the same manner as in Example2-2, except that the mixed solution was prepared so as to include 1.2parts by weight of red-based quantum dots in the red-based dispersionsolution, 8 parts by weight of the green-based fluorescent substance,and 960 parts by weight of the solvent based on 100 parts by weight ofthe polymer resin.

Comparative Example 2-4

A quantum dot sheet having the fibrous-web structure including a singlelayer was manufactured in the same manner as in Example 2-2, except thatthe average thickness of the quantum dot layer was 89 μm to 90 μm. Atthis time, the average particle diameter of the nanofibers constitutingthe quantum dot layer of the quantum dot sheet was in the range of 1,050nm to 1,060 nm.

Experimental Example 4: Measurement of Color Coordinates, ColorReproduction Rate, and Luminance

The color coordinate, the color reproduction rate, and the luminancewere measured in the same manner as in Experimental Example 1 using thequantum dot sheets formed in Examples 2-2 to 2-5 and ComparativeExamples 2-1 to 2-4, and the results are shown in Table 4 below. At thistime, each measurement value represents an average value obtained aftermeasuring five times.

TABLE 4 Color Color coordinates reproduction Luminance ClassificationCIE x CIE y rate (cd/m²) Example 2-2 0.2959 0.3123 102.3% 4,957 Example2-3 0.2955 0.3312 102.9% 4,950 Example 2-4 0.2956 0.3524 103.6% 4,926Example 2-5 0.2962 0.3132 102.1% 4,857 Comparative 0.2894 0.3256  99.1%4,438 Example 2-1 Comparative 0.2961 0.3827 100.6% 4,786 Example 2-2Comparative 0.2967 0.2893 100.8% 4,755 Example 2-3 Comparative 0.29520.3135 101.5% 4,596 Example 2-4

Referring to the experimental results shown in Table 4, in Examples 2-2to 2-5, it was found that the color coordinates satisfied 0.26≤CIEx≤0.32 and 0.30≤CIE y≤0.37 to realize white light, and the colorreproduction rate was 100% or more. In particular, the colorreproduction rate of the non-cadmium-based quantum dots tended to beslightly lower than the color reproduction rate of the cadmium-basedquantum dots. Comparing the color reproduction rates of ComparativeExample 2-1 of a coating film (or a film membrane) with Example 2-2, itwas found that the quantum dot sheet manufactured to have thefibrous-web structure obtained an effect of enhanced color reproductionrate.

In the case of Comparative Example 2-2 in which more than 40 parts byweight of the fluorescent substance were used and Comparative Example2-3 in which less than 10 parts by weight of the fluorescent substancewere used, the CIE y value exceeded 0.37, which made it difficult torealize white light, so that the color reproduction rate and theluminance tended to be lower when compared with Example 2-4.

In the case of Comparative Example 2-4 in which the average particlediameter of the nanofibers exceeded 1,000 nm, when compared with Example2-4, there was no significant influence on the color coordinates and thecolor reproduction rate, whereas the luminance significantly decreasedto less than 4,600 cd/m², and it was determined that the luminancedecreased because the diffuse reflection effect of light decreased.

In the above examples and experimental examples, the BLU to which thequantum dot sheet of the present disclosure is applied may transmitlight of high luminance to the prism sheet without using the diffusionsheet, so that a BLU having a volume (and/or a thickness) reduced asmuch as the volume (and/or a thickness) of the diffusion sheet may beprovided, and the BLU may be applied to an LCD, an LED display, and anLED lighting device requiring high color reproducibility. In addition,since the quantum dot sheet of the present disclosure has thefibrous-web structure, the quantum dot sheet has excellent flexibility,so that the quantum dot sheet can be applied to a flexible display, aflexible lighting device, or the like.

The invention claimed is:
 1. A quantum dot sheet having a fibrous-webstructure, including a quantum dot layer with an average thickness of 3μm to 100 μm having a three-dimensional network structure formed by anaggregate of nanofibers with an average particle diameter of 200 nm to1,000 nm, wherein the nanofibers include 1 to 6 parts by weight ofquantum dots with an average particle diameter of 1 nm to 50 nm based on100 parts by weight of a polymer resin, wherein the polymer resinincludes polyvinylidene fluoride and polyalkylmethacrylate in a ratio of3 to 5:5 to 7 by weight, wherein the quantum dot layer includesred-based quantum dots and yellow-based quantum dots in a ratio of 1:0.8to 2.5 by weight, wherein the red-based quantum dots have aphotoluminescence (PL) wavelength peak of 600 nm to 750 nm and theyellow-based quantum dots have a PL wavelength peak of 550 nm to 600 nm,wherein, when a color coordinate for an area of 1.5 mmØ in the quantumdot sheet is measured using a color coordinate system measurement devicewhere under conditions in which a distance between a blue light sourceand the quantum dot sheet is 0.5 m and a measurement angle is 0.2°, aCIE x color coordinate value ranges from 0.26 to 0.32 and a CIE y colorcoordinate value ranges from 0.30 to 0.37, wherein the quantum dot sheethas a color reproduction rate of 105% or more and a luminance of 5,500cd/m² or more on the basis of a 100% NTSC color gamut based on CIE 1931color coordinates.
 2. The quantum dot sheet of claim 1, wherein thenanofibers further include a fluorescent substance in thethree-dimensional network structure.
 3. The quantum dot sheet of claim2, wherein the quantum dot layer is formed to have the three-dimensionalnetwork structure by forming the aggregate in which the nanofibers arelaminated by electrospinning or electrospraying a mixed solutionincluding the quantum dots, a fluorescent substance, and the polymerresin; and the mixed solution includes the quantum dots and thefluorescent substance in a weight ratio of 1:10 to 1:40.
 4. The quantumdot sheet of claim 2, wherein the fluorescent substance has an averageparticle diameter of 2,000 nm to 30,000 nm; and the fluorescentsubstance includes at least one selected from the group consisting of asilicate-based fluorescent substance, a sulfide-based fluorescentsubstance, a nitrate-based fluorescent substance, a nitride-basedfluorescent substance, and an aluminate-based fluorescent substance. 5.The quantum dot sheet of claim 2, wherein the quantum dots includered-based quantum dots; and the fluorescent substance includes at leastone selected from the group consisting of a green-based fluorescentsubstance and a yellow-based fluorescent substance.
 6. The quantum dotsheet of claim 1, further comprising a support layer or a barrier layerdisposed downstream of the quantum dot layer when viewed from a lighttransmission direction.
 7. The quantum dot sheet of claim 6, furthercomprising a barrier layer disposed upstream of the quantum dot layerwhen viewed from the light transmission direction.
 8. The quantum dotsheet of claim 1, wherein the nanofibers are coated with a barriermaterial.
 9. A backlight unit comprising a quantum dot sheet of claim 1,wherein the quantum dot sheet comprises a quantum dot layer having athree-dimensional network structure formed by an aggregate ofnanofibers, wherein the nanofibers include quantum dots.
 10. A method ofmanufacturing the quantum dot sheet of claim 1, the method comprising: afirst step of preparing a mixed solution including a quantum dotdispersion solution containing quantum dots, a polymer resin, and asolvent; a second step of forming an aggregate in which nanofibers arelaminated by electrospinning or electrospraying the mixed solution on atop surface of a support layer or a barrier layer; and a third step ofdrying the aggregate in which the nanofibers are laminated to form aquantum dot layer having a three-dimensional network structure.
 11. Themethod of claim 10, wherein the mixed solution further includes afluorescent substance.
 12. The method of claim 10, further comprising afourth step of laminating a barrier layer on one surface of the quantumdot layer formed in the third step.
 13. The method of claim 10, furthercomprising separating the quantum dot layer formed in the third stepfrom the support layer or the barrier layer.